In other words, if we buy a 2-day hopper and decided to visit the parks a 3rd day, can we just pay the difference? I'm pretty sure they do this in WDW but not sure about DL.
As long as you decide to do this before the end of the day on the second day you should be able to simply pay the difference. My guess is this would be done just outside of the disneyland gates at guest services.
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